Forget the Silence or River Song or just why bow-ties are so cool – a mystery that has eluded fans for far longer has been solved: why did Christopher Eccleston really leave after one series of Doctor Who?

Speaking at an acting masterclass at the Theatre Royal Haymarket on Wednesday, Eccleston reportedly revealed that it was on-set politics and principles that finally led him to resign. According to Bad Wilf , which has a transcript of the session, Eccleston said he left the show "because I could not get along with the senior people".

"I left because of politics. I did not see eye to eye with them. I didn't agree with the way things were being run. I didn't like the culture that had grown up around the series. So I left, I felt, over a principle."

It's brought an end to a lot of speculation. Ever since Eccleston left the show in 2005 he has dropped several lukewarm hints that there was more to his experience as the Doctor than he was letting on – with fan assumptions being that the BBC either wasn't happy with him or that Eccleston feared he might never regenerate from Doctor Who's typecasting doom if he stayed longer. When asked recently whether he would return for the show's 50th anniversary in 2013 (an episode rumoured to feature past Doctors such as David Tennant) he was clear: "No, never bathe in the same river twice."

A shame, really. For Eccleston's Doctor may have had many faults – looking like an EastEnders extra and bellowing "FANTASTIC!" at every opportunity being two of them – but he was merely a reflection of a show that, at the time, still didn't know what it wanted to be. The first series of the revived Doctor Who – which featured farting aliens – was a world away from the intelligent, populist science-fiction we know it as now. But then, it is thanks to Eccleston that it got this far at all – a big, respectable name who laid the foundations for Tennant to swag away with the show.

At his worst, Eccleston was as cheesy as the lines that were written for him. "I think you need a doctor," he once said, before kissing his companion, Rose. At his best, however – in Steven Moffat's sinister two-parter The Empty Child / The Doctor Dances, for example – he brought warmth, wit and promise. Yes, he didn't really look right, but what he lacked in the Doctor's trademark 'quirk' he made up for with a formidable presence.

He painted a picture of a man always on the run for fear of looking back – who had purged two mighty civilisations and was paying for it every day with his conscience. In essence, despite all the hype of a man who burns at the centre of time, Eccleston's Doctor gave us something human. Given a second chance – or a second series – he could have given us a lot more.